The present invention relates generally to communications and more particularly to systems and methods for wireless communications.
As the Internet continues its development and as workers and consumers increasingly rely on data networking to assist their day-to-day tasks, a need arises to extend network connectivity to locations where there is no convenient connection to a wired infrastructure. Workers desire to send and receive email and access the Internet and their corporate intranet even when they are away from their workstation. Consumers wish to establish home networks without costly and cumbersome wiring. Accordingly, wireless communication standards have evolved including the IEEE 802.11 family.
The current IEEE 802.11a standard allows for wireless communicates at speeds between 6 Mbps and 54 Mbps. It is desirable to further increase these speeds to accommodate delivery of multimedia wireless services and facilitate outdoor wireless bridging between indoor networks. It is also desirable to accommodate the increased data rates by increasing spectral efficiency rather than by increasing bandwidth.
One known way of increasing spectral efficiency is the use of MIMO (Multiple Input Multiple Output) processing techniques. MIMO techniques take advantage of multiple antennas (or multiple polarizations of the same antenna) at the transmitter and receiver to access multiple channel inputs and channel outputs and thereby define multiple spatial subchannels that occupy the same bandwidth but nonetheless are capable of carrying independent data streams. The delineation of the multiple spatial subchannels may involve weighting of the antenna inputs at the transmitter end and/or weighting of the antenna outputs at the receiver end. For further information on MIMO techniques, see U.S. Pat. No. 6,377,631.
It is desirable to apply MIMO techniques to IEEE 802.11 systems to increase data carrying capacity, but there are obstacles to overcome. The 802.11 standards do not currently specify MIMO transmission techniques. In particular, MIMO transmission techniques preferably take advantage of an estimate of the MIMO channel response. The MIMO channel response is represented by a matrix composed of elements corresponding to each combination of channel input and channel output. By contrast, 802.11a, for example, provides only for estimating a conventional channel response that assumes a single input and a single output.
It would be desirable to maximize the usage of 802.11 techniques and components in a MIMO wireless communication system while still meeting the MIMO requirement of obtaining a MIMO matrix channel estimate. It is furthermore generally desirable to use MIMO techniques to increase the capacity of 802.11 networks.